Internal combustion engines, including diesel engines, gasoline engines, gaseous fuel-powered engines, and other engines known in the art exhaust a complex mixture of air pollutants. These air pollutants are generally composed of particulates and gaseous compounds including nitrogen oxides (NOx) among others. Due to increased awareness of the environment, exhaust emission standards have become more stringent, and the amounts of particulates and NOx emitted into the atmosphere by an engine may be regulated depending on the type of the engine, size of the engine, class of the engine, and the like.
In order to comply with the regulation of particulates and NOx, some engine manufacturers have implemented a strategy called selective catalytic reduction (SCR), which is a process where a reagent, most commonly urea ((NH2)2CO), or a water/urea solution, is selectively injected into the exhaust gas stream of an engine and absorbed onto a downstream substrate. The injected urea solution decomposes into ammonia (NH3), which reacts with NOx in the exhaust gas to form water (H2O) and diatomic nitrogen (N2). However, because an excess in either the NOx or the urea injected may result in undesirable emissions, the urea dosage must be carefully controlled.
Aftertreatment models have been developed to help SCR systems estimate the appropriate amount of urea to be injected for different conditions to result in better NOx conversion efficiencies. One such type of model is a model predictive control (MPC) which generally assumes a certain NOx quantity for a given model of the exhaust system and guides the SCR process based on this quantity. While aftertreatment models may provide some means for estimating appropriate urea dosing values and improving the overall NOx conversion efficiency, there is still room for improvement.
In particular, the quantity of NOx that is exhausted from an engine, or the engine NOx output value, is not only tied to reducing pollutants, but it is also directly tied to the fuel efficiency of the associated engine. For instance, an increase in fuel efficiency results in an increase in engine NOx output, and a decrease in fuel efficiency results in a decrease in engine NOx output. Conventional MPC models may estimate optimal urea dosing values, but there are still no models which also estimate optimal engine NOx output for the purposes of improving fuel efficiency.
The present disclosure is directed at addressing one or more of the deficiencies set forth above.